Tailoring Colon Cancer Screening

October 29, 2009

Guidelines for Colorectal Cancer Screening and the Recent Evidence Behind Them

Nazia Hasan, MD MPH

Faculty peer reviewed

For most residents, screening for colorectal cancer (CRC) may seem as established as that for breast and cervical cancer. In reality, the use of CRC screening has only recently approached that of screening for those other malignancies. We have seen recently changes to the CRC screening guidelines last published by The American College of Gastroenterology in 2000. The updated screening guidelines for colorectal cancer became available in the March 2009 issue of The American Journal of Gastroenterology.

Along with changes in the timing and modalities used for CRC screening, the goal of screening has also been transformed. Screening efforts have shifted focus to favor cancer prevention tests over cancer detection tests. This blog series aims to review the updated guidelines for CRC screening illustrated through cases.

CASE 1:

A 46 year old African-American male presents for routine health maintenance. He has never had any colorectal cancer screening, denies a personal or family history of GI disorders including malignancy, and is currently asymptomatic.

What modality is the most preferred by the ACG for CRC screening in this patient?

Recommendations for screening continue to support offering screening at age 50 for average-risk persons (1). However there is evidence to suggest screening for African Americans should be initiated at age 45 due to the high incidence of colorectal cancer and a greater prevalence of proximal or right-sided polyps and cancerous lesions in this population (2).

An approach to screening regarded as ‘menu-of-options’ was initially established by the American Cancer Society in 1997 (1). While the ACG endorses this approach, it offers an alternative by having colonoscopy every 10 years as the ‘preferred’ strategy (Grade 1B rec-see Appendix)(1). The rationale for this is based on a trial by Inadomi, et. al. in which patients were more likely to undergo screening with the preferred strategy approach compared with the “menu of options” as it simplifies and shortens the discussion for screening (3).

In addition, the ACG supports the division of screening tests into cancer prevention tests (able to identify polyps and cancer) and cancer detection tests (lower sensitivity especially for polyps) with preference for prevention tests (1). The following are alternative tests suggested by the ACG if economic limitations or patient preference preclude colonoscopy every 10 years:

With evidence from recent trials, a relatively new mode of screening, CT colonography has replaced the use of double-contrast barium enema. Johnson et al. sought to compare the accuracy of CT colonography vs. optical colonoscopy for CRC screening. Using CT colonography, the authors were able to identify 90% of cancers and adenomas >10mm, however this method was not as sensitive for polyps smaller than 10mm, which may or may not be inconsequential and this technique missed flat/depressed adenomas, which may represent 10% of precancerous lesions. (4) Two primary concerns emerge from this relatively new mode of screening. Firstly, CT colonography may reveal extra-colonic findings, which may or may not be clinically significant, but may result in lengthy and costly evaluations (5). Secondly, if utilized every five years, as recommended, the cumulative radiation doses could become a concern for carcinogenesis (5). Regardless, this mode of screening offers an alternative for patients who refuse screening colonoscopy.

Note, the USPSTF concludes that the evidence is insufficient to assess the benefits and harms of CT colonography and fecal DNA testing as screening modalities for colorectal cancer. It remains a Grade I recommendation under their guidelines (6) (See appendix).

Thus, for this 46 year old African American male at average risk for CRC, under the new ACG guidelines, screening should be started at age 45 with colonoscopy as the preferred method.

APPENDIX

Table 1. Grading Recommendations: ACG1

Table 2. Grading Recommendations: USPSTF6

Grade

Definition

Suggestions for Practice

A

The USPSTF recommends the service. There is high certainty that the net benefit is substantial.

Offer or provide this service.

B

The USPSTF recommends the service. There is high certainty that the net benefit is moderate or there is moderate certainty that the net benefit is moderate to substantial.

Offer or provide this service.

C

The USPSTF recommends against routinely providing the service. There may be considerations that support providing the service in an individual patient. There is at least moderate certainty that the net benefit is small.

Offer or provide this service only if other considerations support the offering or providing the service in an individual patient.

D

The USPSTF recommends against the service. There is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits.

Discourage the use of this service.

I Statement

The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of the service. Evidence is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined.

Read the clinical considerations section of USPSTF Recommendation Statement. If the service is offered, patients should understand the uncertainty about the balance of benefits and harms.

Dr. Hasan is a 3rd year internal medicine resident at NYU Medical Center.

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